#include <iostream>
using namespace std;
long double a[110];
int main()
{
    a[0]=4, a[1]=3;
    for(int i=2;i<=100;++i) a[i]=(19*a[i-1]-12*a[i-2])*0.25;
    int n;
    while (cin>>n) cout<<a[n]<<endl;
}